/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.beanutils.converters;

import java.io.IOException;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.beanutils.ConversionException;
import org.apache.commons.beanutils.Converter;

/**
 * Generic {@link Converter} implementaion that handles conversion to and from <b>array</b> objects.
 * <p>
 * Can be configured to either return a <i>default value</i> or throw a <code>ConversionException</code> if a conversion error occurs.
 * <p>
 * The main features of this implementation are:
 * <ul>
 * <li><b>Element Conversion</b> - delegates to a {@link Converter}, appropriate for the type, to convert individual elements of the array. This
 * leverages the power of existing converters without having to replicate their functionality for converting to the element type and removes the need
 * to create a specifc array type converters.</li>
 * <li><b>Arrays or Collections</b> - can convert from either arrays or Collections to an array, limited only by the capability of the delegate
 * {@link Converter}.</li>
 * <li><b>Delimited Lists</b> - can Convert <b>to</b> and <b>from</b> a delimited list in String format.</li>
 * <li><b>Conversion to String</b> - converts an array to a <code>String</code> in one of two ways: as a <i>delimited list</i> or by converting the
 * first element in the array to a String - this is controlled by the {@link ArrayConverter#setOnlyFirstToString(boolean)} parameter.</li>
 * <li><b>Multi Dimensional Arrays</b> - its possible to convert a <code>String</code> to a multi-dimensional arrays, by embedding
 * {@link ArrayConverter} within each other - see example below.</li>
 * <li><b>Default Value</b></li>
 * <ul>
 * <li><b><i>No Default</b></i> - use the {@link ArrayConverter#ArrayConverter(Class, Converter)} constructor to create a converter which throws a
 * {@link ConversionException} if the value is missing or invalid.</li>
 * <li><b><i>Default values</b></i> - use the {@link ArrayConverter#ArrayConverter(Class, Converter, int)} constructor to create a converter which
 * returns a <i>default value</i>. The <i>defaultSize</i> parameter controls the <i>default value</i> in the following way:</li>
 * <ul>
 * <li><i>defaultSize &lt; 0</i> - default is <code>null</code></li>
 * <li><i>defaultSize = 0</i> - default is an array of length zero</li>
 * <li><i>defaultSize &gt; 0</i> - default is an array with a length specified by <code>defaultSize</code> (N.B. elements in the array will be
 * <code>null</code>)</li>
 * </ul>
 * </ul> </ul>
 * 
 * <h3>Parsing Delimited Lists</h3>
 * This implementation can convert a delimited list in <code>String</code> format into an array of the appropriate type. By default, it uses a comma
 * as the delimiter but the following methods can be used to configure parsing:
 * <ul>
 * <li><code>setDelimiter(char)</code> - allows the character used as the delimiter to be configured [default is a comma].</li>
 * <li><code>setAllowedChars(char[])</code> - adds additional characters (to the default alphabetic/numeric) to those considered to be valid token
 * characters.
 * </ul>
 * 
 * <h3>Multi Dimensional Arrays</h3>
 * It is possible to convert a <code>String</code> to mulit-dimensional arrays by using {@link ArrayConverter} as the element {@link Converter} within
 * another {@link ArrayConverter}.
 * <p>
 * For example, the following code demonstrates how to construct a {@link Converter} to convert a delimited <code>String</code> into a two dimensional
 * integer array:
 * <p>
 * 
 * <pre>
 * // Construct an Integer Converter
 * IntegerConverter integerConverter = new IntegerConverter();
 * 
 * // Construct an array Converter for an integer array (i.e. int[]) using
 * // an IntegerConverter as the element converter.
 * // N.B. Uses the default comma (i.e. &quot;,&quot;) as the delimiter between individual numbers
 * ArrayConverter arrayConverter = new ArrayConverter(int[].class, integerConverter);
 * 
 * // Construct a &quot;Matrix&quot; Converter which converts arrays of integer arrays using
 * // the pre-ceeding ArrayConverter as the element Converter.
 * // N.B. Uses a semi-colon (i.e. &quot;;&quot;) as the delimiter to separate the different sets of numbers.
 * //      Also the delimiter used by the first ArrayConverter needs to be added to the
 * //      &quot;allowed characters&quot; for this one.
 * ArrayConverter matrixConverter = new ArrayConverter(int[][].class, arrayConverter);
 * matrixConverter.setDelimiter(';');
 * matrixConverter.setAllowedChars(new char[] { ',' });
 * 
 * // Do the Conversion
 * String matrixString = &quot;11,12,13 ; 21,22,23 ; 31,32,33 ; 41,42,43&quot;;
 * int[][] result = (int[][]) matrixConverter.convert(int[][].class, matrixString);
 * </pre>
 * 
 * @version $Revision: 640131 $ $Date: 2008-03-23 02:10:31 +0000 (Sun, 23 Mar 2008) $
 * @since 1.8.0
 */
public class ArrayConverter extends AbstractConverter {

    private Object defaultTypeInstance;
    private Converter elementConverter;
    private int defaultSize;
    private char delimiter = ',';
    private char[] allowedChars = new char[] { '.', '-' };
    private boolean onlyFirstToString = true;

    // ----------------------------------------------------------- Constructors

    /**
     * Construct an <b>array</b> <code>Converter</code> with the specified <b>component</b> <code>Converter</code> that throws a
     * <code>ConversionException</code> if an error occurs.
     * 
     * @param defaultType
     *            The default array type this <code>Converter</code> handles
     * @param elementConverter
     *            Converter used to convert individual array elements.
     */
    public ArrayConverter(Class defaultType, Converter elementConverter) {
        super();
        if (defaultType == null) {
            throw new IllegalArgumentException("Default type is missing");
        }
        if (!defaultType.isArray()) {
            throw new IllegalArgumentException("Default type must be an array.");
        }
        if (elementConverter == null) {
            throw new IllegalArgumentException("Component Converter is missing.");
        }
        this.defaultTypeInstance = Array.newInstance(defaultType.getComponentType(), 0);
        this.elementConverter = elementConverter;
    }

    /**
     * Construct an <b>array</b> <code>Converter</code> with the specified <b>component</b> <code>Converter</code> that returns a default array of the
     * specified size (or <code>null</code>) if an error occurs.
     * 
     * @param defaultType
     *            The default array type this <code>Converter</code> handles
     * @param elementConverter
     *            Converter used to convert individual array elements.
     * @param defaultSize
     *            Specifies the size of the default array value or if less than zero indicates that a <code>null</code> default value should be used.
     */
    public ArrayConverter(Class defaultType, Converter elementConverter, int defaultSize) {
        this(defaultType, elementConverter);
        this.defaultSize = defaultSize;
        Object defaultValue = null;
        if (defaultSize >= 0) {
            defaultValue = Array.newInstance(defaultType.getComponentType(), defaultSize);
        }
        setDefaultValue(defaultValue);
    }

    /**
     * Set the delimiter to be used for parsing a delimited String.
     * 
     * @param delimiter
     *            The delimiter [default ',']
     */
    public void setDelimiter(char delimiter) {
        this.delimiter = delimiter;
    }

    /**
     * Set the allowed characters to be used for parsing a delimited String.
     * 
     * @param allowedChars
     *            Characters which are to be considered as part of the tokens when parsing a delimited String [default is '.' and '-']
     */
    public void setAllowedChars(char[] allowedChars) {
        this.allowedChars = allowedChars;
    }

    /**
     * Indicates whether converting to a String should create a delimited list or just convert the first value.
     * 
     * @param onlyFirstToString
     *            <code>true</code> converts only the first value in the array to a String, <code>false</code> converts all values in the array into a
     *            delimited list (default is <code>true</code>
     */
    public void setOnlyFirstToString(boolean onlyFirstToString) {
        this.onlyFirstToString = onlyFirstToString;
    }

    /**
     * Return the default type this <code>Converter</code> handles.
     * 
     * @return The default type this <code>Converter</code> handles.
     */
    protected Class getDefaultType() {
        return defaultTypeInstance.getClass();
    }

    /**
     * Handles conversion to a String.
     * 
     * @param value
     *            The value to be converted.
     * @return the converted String value.
     * @throws Throwable
     *             if an error occurs converting to a String
     */
    protected String convertToString(Object value) throws Throwable {

        int size = 0;
        Iterator iterator = null;
        Class type = value.getClass();
        if (type.isArray()) {
            size = Array.getLength(value);
        } else {
            Collection collection = convertToCollection(type, value);
            size = collection.size();
            iterator = collection.iterator();
        }

        if (size == 0) {
            return (String) getDefault(String.class);
        }

        if (onlyFirstToString) {
            size = 1;
        }

        // Create a StringBuffer containing a delimited list of the values
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < size; i++) {
            if (i > 0) {
                buffer.append(delimiter);
            }
            Object element = iterator == null ? Array.get(value, i) : iterator.next();
            element = elementConverter.convert(String.class, element);
            if (element != null) {
                buffer.append(element);
            }
        }

        return buffer.toString();

    }

    /**
     * Handles conversion to an array of the specified type.
     * 
     * @param type
     *            The type to which this value should be converted.
     * @param value
     *            The input value to be converted.
     * @return The converted value.
     * @throws Throwable
     *             if an error occurs converting to the specified type
     */
    protected Object convertToType(Class type, Object value) throws Throwable {

        if (!type.isArray()) {
            throw new ConversionException(toString(getClass()) + " cannot handle conversion to '" + toString(type) + "' (not an array).");
        }

        // Handle the source
        int size = 0;
        Iterator iterator = null;
        if (value.getClass().isArray()) {
            size = Array.getLength(value);
        } else {
            Collection collection = convertToCollection(type, value);
            size = collection.size();
            iterator = collection.iterator();
        }

        // Allocate a new Array
        Class componentType = type.getComponentType();
        Object newArray = Array.newInstance(componentType, size);

        // Convert and set each element in the new Array
        for (int i = 0; i < size; i++) {
            Object element = iterator == null ? Array.get(value, i) : iterator.next();
            // TODO - probably should catch conversion errors and throw
            //        new exception providing better info back to the user
            element = elementConverter.convert(componentType, element);
            Array.set(newArray, i, element);
        }

        return newArray;
    }

    /**
     * Returns the value unchanged.
     * 
     * @param value
     *            The value to convert
     * @return The value unchanged
     */
    protected Object convertArray(Object value) {
        return value;
    }

    /**
     * Converts non-array values to a Collection prior to being converted either to an array or a String. </p>
     * <ul>
     * <li>{@link Collection} values are returned unchanged</li>
     * <li>{@link Number}, {@link Boolean} and {@link java.util.Date} values returned as a the only element in a List.</li>
     * <li>All other types are converted to a String and parsed as a delimited list.</li>
     * </ul>
     * 
     * <strong>N.B.</strong> The method is called by both the {@link ArrayConverter#convertToType(Class, Object)} and
     * {@link ArrayConverter#convertToString(Object)} methods for <i>non-array</i> types.
     * 
     * @param type
     *            The type to convert the value to
     * @param value
     *            value to be converted
     * @return Collection elements.
     */
    protected Collection convertToCollection(Class type, Object value) {
        if (value instanceof Collection) {
            return (Collection) value;
        }
        if (value instanceof Number || value instanceof Boolean || value instanceof java.util.Date) {
            List list = new ArrayList(1);
            list.add(value);
            return list;
        }

        return parseElements(type, value.toString());
    }

    /**
     * Return the default value for conversions to the specified type.
     * 
     * @param type
     *            Data type to which this value should be converted.
     * @return The default value for the specified type.
     */
    protected Object getDefault(Class type) {
        if (type.equals(String.class)) {
            return null;
        }

        Object defaultValue = super.getDefault(type);
        if (defaultValue == null) {
            return null;
        }

        if (defaultValue.getClass().equals(type)) {
            return defaultValue;
        } else {
            return Array.newInstance(type.getComponentType(), defaultSize);
        }

    }

    /**
     * Provide a String representation of this array converter.
     * 
     * @return A String representation of this array converter
     */
    public String toString() {
        StringBuffer buffer = new StringBuffer();
        buffer.append(toString(getClass()));
        buffer.append("[UseDefault=");
        buffer.append(isUseDefault());
        buffer.append(", ");
        buffer.append(elementConverter.toString());
        buffer.append(']');
        return buffer.toString();
    }

    /**
     * <p>
     * Parse an incoming String of the form similar to an array initializer in the Java language into a <code>List</code> individual Strings for each
     * element, according to the following rules.
     * </p>
     * <ul>
     * <li>The string is expected to be a comma-separated list of values.</li>
     * <li>The string may optionally have matching '{' and '}' delimiters around the list.</li>
     * <li>Whitespace before and after each element is stripped.</li>
     * <li>Elements in the list may be delimited by single or double quotes. Within a quoted elements, the normal Java escape sequences are valid.</li>
     * </ul>
     * 
     * @param type
     *            The type to convert the value to
     * @param value
     *            String value to be parsed
     * @return List of parsed elements.
     * 
     * @throws ConversionException
     *             if the syntax of <code>svalue</code> is not syntactically valid
     * @throws NullPointerException
     *             if <code>svalue</code> is <code>null</code>
     */
    private List parseElements(Class type, String value) {

        if (log().isDebugEnabled()) {
            log().debug("Parsing elements, delimiter=[" + delimiter + "], value=[" + value + "]");
        }

        // Trim any matching '{' and '}' delimiters
        value = value.trim();
        if (value.startsWith("{") && value.endsWith("}")) {
            value = value.substring(1, value.length() - 1);
        }

        try {

            // Set up a StreamTokenizer on the characters in this String
            StreamTokenizer st = new StreamTokenizer(new StringReader(value));
            st.whitespaceChars(delimiter, delimiter); // Set the delimiters
            st.ordinaryChars('0', '9'); // Needed to turn off numeric flag
            st.wordChars('0', '9'); // Needed to make part of tokens
            for (int i = 0; i < allowedChars.length; i++) {
                st.ordinaryChars(allowedChars[i], allowedChars[i]);
                st.wordChars(allowedChars[i], allowedChars[i]);
            }

            // Split comma-delimited tokens into a List
            List list = null;
            while (true) {
                int ttype = st.nextToken();
                if ((ttype == StreamTokenizer.TT_WORD) || (ttype > 0)) {
                    if (st.sval != null) {
                        if (list == null) {
                            list = new ArrayList();
                        }
                        list.add(st.sval);
                    }
                } else if (ttype == StreamTokenizer.TT_EOF) {
                    break;
                } else {
                    throw new ConversionException("Encountered token of type " + ttype + " parsing elements to '" + toString(type) + ".");
                }
            }

            if (list == null) {
                list = Collections.EMPTY_LIST;
            }
            if (log().isDebugEnabled()) {
                log().debug(list.size() + " elements parsed");
            }

            // Return the completed list
            return (list);

        } catch (IOException e) {

            throw new ConversionException("Error converting from String to '" + toString(type) + "': " + e.getMessage(), e);

        }

    }

}
